1. Field of the Invention
The present disclosure relates to a sensor thin film transistor (“TFT”) and a TFT substrate having the same.
2. Description of the Related Art
With the development of information devices, an introduction of an efficient input means as an interface between a human being and a machine is in demand. Touch screen panels that serve as an input means and operate as a display means when the input function is not used are of interest.
A touch screen panel may be separately attached on an image display panel of an information display device or may be included in the image display panel of the information display device. When the touch screen panel is separately attached on the image display panel, image display quality is typically lowered due to low transmissivity of the information display device. Accordingly, the touch screen panel included in the image display panel has been developed. Touch screen panels may be classified into a light sensing type, an ultrasonic type, a capacitance type, and a resistive type. The light sensing type is suitable for the touch screen panel included in the image display panel.
A touch screen panel of the light sensing type includes a driving thin film transistor for driving pixels and a light sensor for sensing light. A semiconductor channel of the light sensor is made of amorphous silicon formed by a high-temperature deposition process, like a semiconductor channel of the driving TFT. However, since a signal-to-noise (S/N) ratio of the light sensor is low, the light sensitivity of the light sensor is reduced. Also, it is difficult to improve the S/N ratio of the light sensor because background noise is also amplified when a signal is amplified.